Our Experiment

1
Imaging Energetic Nuclear Particles Author
Cassandra Niman UC San Diego Advisor Dr. Robert
Tribble REU at the Cyclotron Institute Texas
AM University, 2007

• Semiconductor Detectors
• Detectors are reverse biased diodes made from
  doped semiconductors
• The non-conducting depletion zone in the
  pn-junction of the diode is
• where we can detect particle interactions
• The current produced from the particle
  interaction with the detector can
• be used to find the position and energy of the
  charged particles
• 16 strip detector
• Front - 16 resistive strips of
• silicon for position signals
• Back - One non-resistive sheet of
• silicon for an energy signal

Our Experiment Purpose To test the
resolution capabilities of a prototype four
corner position sensitive silicon detector
when used with a radioactive nuclear beam of
46V. Also, to determine the energy and position
resolution capabilities and the response in
terms of position linearity for different
shaping times of the amplifier. The
Setup The Detector Mask
Position Calculations
Results Alpha Source Measurements
46V Beam Measurements at MARS
How Does MARS Work?
4 Corner Detector with Mask
Slits

• Below is position imaging by four single sided
  16
• silicon strip detectors
• These are the results of the 12N experiment at
  the
• Momentum Achromat Recoil Separator (MARS)

Strip Detector

• Silicon detectors are also used to look at the
  products from
• nuclear reactions

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2in

• Primary beam from K500
• Reaction in the gas cell to get a secondary beam
  
• Separate the beam by the magnetic rigidity, Br
  p/q, using
• dipole D1
• Stop the primary beam with a Faraday cup in the
  coffin
• Select the desired momentum of the beam with
  slits in
• the coffin
• Quadrupole, Q3 and dipole D2 make a momentum
  achromat to
• get a parallel beam into the velocity filter

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0.15in

• The method of particle identification shown
  above uses a
• telescope and looks at EdE Etotal vs. dE
• Above right is the dE-Etotal plot showing the
  products of the
• 12N 12C reaction at 12A MeV

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0.04in for all
The design of the mask allows us to see the
position resolution capabilities of the detector.
Even in the region of the mask with the smallest
spacing of holes, the holes are distinguishable.
Using the alpha source gives very poor position
resolution (gt5mm)

• Velocity Filter and dipole D3 make mass
  selection,
• m/q in the y-direction

• Washington University uses double sided 32 x 32
  silicon strip
• detectors for position reconstruction
• Below are the results of the 10C experiment at
  MARS
• at Texas AM

Position signal shaping time 1µs Energy signal
shaping time 1µs
Position signal shaping time 1µs Energy signal
shaping time 3µs

• Using a resistive silicon strip detector we can
  see the
• energy lost by the beam in the detector vs. y
  ( vertical
• position)
• We can pick out a particular beam by closing the
  slits in
• the y-direction
• For this experiment we were trying to get a beam
  of 46V
• Above the full beam after going through MARS
• Below the beam after the slits are used to
  select 46V with
• 97 purity

Comparing results with different energy shaping
times there seems to be less distortion with a
larger energy shaping time.
Position signal shaping time 6µs Energy signal
shaping time 6µs
Position signal shaping time 3µs Energy signal
shaping time 6µs

• We tested the four corner
• detector as a target
• detector at the end of the
• MARS beam line
• For this experiment we
• were trying to get a beam
• of 18Ne
• The four corner detector
• gives better position
• resolution, 1mm, than
• the strip detectors whose
• position resolution is
• limited to the width
• of the strip, 3mm

Comparing results with the same energy shaping
time of 6µs the better position resolution is
found when using a smaller shaping time.
Also see the results for the 18Ne tests to the
far left bottom. This shows position and energy
resolution of this detector.